No abstract

About 10,000 tons of chrysotile per year are used in the Federal Republic of Germany for the production of friction materials. During brake repair an unknown number of approximately 300,000 mechanics in automobile service stations are exposed to asbestos dust. In a field study, asbestos fiber concentrations during brake repair were measured. Occupational histories and chest X-rays of brake service mechanics are being examined. Ninety dust measurements in 76 service stations were made by phase contrast microscopy and by scanning transmission electron microscopy. By electron microscopy, extremely fine chrysotile fibers with lengths less than 5 microns were identified in brake drum dust. Fibers with lengths greater than or equal to 5 microns constituted less than 1% of all chrysotile fibers counted in brake drum dust. Short-term asbestos dust exposures were measured by light microscopy in 101 personal samples during blowing out of brakes, and grinding and turning of brake linings. During blowing out of car brakes, as well as during grinding of brake linings, the product of fiber concentration with length greater than 5 microns and sampling time amounted to about 4-5 fibers/ml X min corresponding to a concentration of 10(6) fibers/m3 over 4-5 min. For trucks and buses higher amounts of 5-10 X 10(6) fibers/m3 X min were observed during these operations. From occupational histories of 210 vehicle mechanics, an average duration of employment of mean +/- s = 21 +/- 10 years and a mean cumulative fiber dose of mean +/- s = (0.54 +/- 1.1) X 10(6) fibers/m3 X years were calculated.

In a mesothelioma case-control study, asbestos and other mineral fibers from lung burden were examined as causal factors. Diagnosis was confirmed by a panel of pathologists. For 66 cases and 66 controls from hospitals in five German towns, lung tissue fiber analysis by transmission electron microscopy was available. Control patients were treated by a surgical lung resection mostly because of lung cancer. For chrysotile and other mineral fibers a significantly increased odds ratio (OR) was not observed. A clear dose-response relationship was demonstrated for the concentration CA of amphibole fibers longer than 5 microm. Between 0.025 and 2.5 fibers/microg dry weight (f/microg) the relationship can be approximated as OR = CA/(0. 025 f/microg). Similar but less distinct dose-response relationships were found in a Canadian and an Australian study. It is concluded that among German mesothelioma patients factors not associated with amphibole fiber concentration are not predominating.

Background This study examines the role of occupational factors in the development of diffuse malignant mesothelioma with special emphasis on the dose±response relationship for asbestos and on the exposure to man-made vitreous ®bers (MMVFs). Methods One hundred and twenty-®ve male cases, diagnosed by a panel of pathologists, were personally interviewed concerning their occupational and smoking history. The same number of population controls (matched for sex, age and region of residence) underwent similar interviews by trained interviewers. Odds ratios (OR) were calculated for an expert-based exposure index using conditional logistic regression. Results Exposure to asbestos shows the expected sharp gradient with an OR of about 45 for a cumulative exposure b 1X5 ®ber years (arithmetic mean 16 ®ber years). A signi®cant OR was calculated even for the lowest exposure category``b 0 ± 0X15 ®ber years''. Although the mean cumulative exposure to MMVF is roughly 10% of the exposure to asbestos, an increased OR is observed in an ever/never evaluation. This observation is heavily hampered by methodical problems. A corresponding case±control study was performed using a lung tissue ®ber analysis in addition to interviews. Both interviews and the lung tissue analysis yielded similar OR levels between the reference and the maximum exposure intervals.Conclusions Despite a possible in¯uence as a result of selection and information bias, our results con®rm the previously reported observation of a distinct dose±response relationship even at levels of cumulative exposure below 1 ®ber year. Moreover, the study con®rms that asbestos is a relevant confounder for MMVF. A causal relationship between exposure to MMVF and mesothelioma could neither be detected nor excluded, as in other studies.